1. Field of the Invention
The invention relates to a metal part presenting an annular portion containing fibrous coaxial annular reinforcement in the form of a winding of composite material embedded in a metal matrix. More particularly, the invention relates to fabricating such a part that benefits from improved strength. The invention also provides a metal part containing such coaxial annular reinforcement.
2. Description of the Related Art
It is known to reduce the weight of an annular metal part while ensuring that it presents very great strength in tangential compression or traction, by incorporating fibers of composite material, such as ceramic fibers for example, in the mass of metal. By way of example, the ceramic may be a yarn of silicon carbide presenting compression or traction strength that is greater than that of a metal, such as titanium for example.
In order to obtain such a part, it is possible to wind a yarn of metal-coated ceramic inside a blank for the part. For example, document FR 2 886 290 proposes making the winding directly on a portion of the blank that acts as a winding mandrel. That is entirely conventional “external” winding. More precisely, that portion comprises two shoulders. The radially-inner shoulder forms a lateral bearing surface for winding. The adjacent cylindrical portion forms the base surface on which the winding is made. In right cross-section, the winding is rectangular in shape. After winding, the blank has additional metal portions applied thereto, in particular an outer ring and a lateral cover presenting a tenon that comes into contact with the winding. The assembly is then subjected to a step of hot isostatic compression during which the cover in particular is deformed so that the winding is compressed by the tenon. The operation of hot isostatic compression is itself known; it consists of placing the above-mentioned assembly in a box and in subjecting the assembly for several hours to a high pressure of the order of 1000 bar and to a temperature of the order of 1000° C. After this operation, the part, now in the form of a single block, is machined to have the desired shape and dimensions. Generally, the various portions of the blank and the sheath of the ceramic yarn are made of the same metal so that the finished part is provided with a wound composite insert that is embedded in a uniform metal matrix.
The zone that is reinforced by the winding is generally rectangular in right cross-section. In order to reduce the weight of the part and increase its traction/compression strength in the tangential direction, it is desirable for the reinforced zone that is surrounded by portions made exclusively of metal to occupy a volume that is as large as possible.
This arrangement with an insert of rectangular right section cannot be completely satisfactory depending on the direction of the forces that are applied to the part. Although the strength of the fibers is excellent tangentially, both in traction and in compression, it is less than the strength of the pure metal when forces are applied in a direction that extends across the fibers. As examples, this applies in particular when the annular part as fabricated in this way is a rotary part fitted with blades, such as a turbine disk, in particular for an airplane turbojet. Another part that is subjected to transverse forces is the “rotary sleeve” that is connected to the actuators in a landing gear mechanism.
With a part having a winding of rectangular right cross-section, it is possible for breakage to occur in the outside portion of the reinforced zone.